In many industrial processes, in heat-generating procedures, and in the use of steam for power purposes and the like, cooling is required and this is usually provided by heat transfer to cooling air or cooling water. When water is employed for this purpose, closed circuits are used to conserve water and to avoid thermal pollution of streams, lakes, etc. Also, various chemicals may be dissolved in the cooling water to prevent corrosion and for other purposes.
Various expedients have been employed, depending upon the application conditions, to continuously cool the water which has been heated in serving its cooling function. One commonly used type of apparatus for continuously cooling the circulating water is the wet type cooling tower which is essentially an evaporative cooler wherein the hot water is continuously supplied to a fill media which provides a very large wet surface area over which air is passed to evaporate a portion of the water which results in the cooling of the water which passes downwardly through the fill to a sump for reuse. Make-up water in amounts sufficient to replace that evaporated in the cooling tower is usually supplied to the body of cooled water in the sump or other reservoir.
The air blown through the cooling tower is exhausted to the atmosphere, usually upwardly at the top of the tower. In an efficiently designed and operating cooling tower, the exhaust air is at least saturated with water. Cooling tower design criteria necessarily include consideration of ambient air conditions at the location of use of the tower, the temperature and humidity of the air greatly influencing not only the evaporating efficiency but also the absorption of the water by the ambient air from the tower exhaust. A pollution problem results when the ambient air conditions are such that the moisture contained in the tower exhaust air is not only not readily dissipated in the atmosphere but is condensed or otherwise affected to form liquid particles which, together with other similar liquid droplets that may be entrained in the exhaust air, form a visible fog stream or "plume". Again, so long as this plume continues to rise and the droplets are re-evaporated and the moisture thus dissipated into the atmosphere, there is no problem. However, if the plume is not sufficiently buoyant, or loses a degree of buoyancy after passing from the cooling tower, the fog, which may contain troublesome chemicals, may flow to and along the ground, possibly interfering with vision on streets or causing damage or annoyance by wetting the surroundings of the tower. Air movements at the location of the tower may aggravate this problem.
The ambient air conditions which tend to cause plume formation are low temperatures and high relative humidity. The chilling of the exhaust air as it leaves the tower causes condensation of water and loss of buoyancy of the body of exhaust air, both of these changes tending to cause plume formation. High relative humidity of the atmosphere results in slow absorption of the water load of the exhaust air by the atmosphere, contributing to the pluming by failing to evaporate moisture in the liquid state in the exhaust air body.
The object of the invention is to provide a wet cooling tower system which incorporates means for providing operating conditions as required by ambient air conditions to avoid exhaust air plume formation. More specifically, the object of the invention is to provide means for reducing the temperature of the cooling tower influent hot water and/or increasing the temperature of the tower inlet air to limit the magnitude and nature of the water load of the exhaust air as required by ambient air conditions to avoid pluming.